An open-ended ring that fits into a groove on the outer diameter of a piston in a reciprocating engine such as an internal combustion engine or steam engine.
The main function of piston rings is to prevent the oil getting into the combustion chamber and combustion gases getting into the oil. They also prevent the piston from contacting the sides of the cylinder and so reduce friction.
Cold-Stuck Piston Ring
A piston ring that is stuck when the piston and ring are at room temperature, but inspection shows that it was free during engine operation.
A cold-stuck piston ring cannot be moved with moderate finger pressure. It is characterized by a polished face over its entire circumference, indicating essentially no blowby passed over the outside of the ring during operation.
Piston rings placed in the upper part of a piston to seal against loss of compression pressure and against gas blowing.
Free Piston Ring
A piston ring that will fall in its groove under its own weight when the piston, with the ring in a horizontal plane, is turned 90 degrees.
A narrow groove in the top land used in some pistons to help control heat getting to the top ring. It actually fills with carbon in normal operation and limits heat flow to the ring.
Hot-Stuck Piston Ring
A piston ring that is stuck when the piston and ring are at room temperature, and inspection shows that it was stuck during engine operation.
The portion of the ring that is stuck cannot be moved with moderate finger pressure. A hot-stuck ring is characterized by varnish or carbon across some portion of its face, indicating that portion of the ring was not contacting the cylinder wall during engine operation.
A dowel or pin used to keep piston rings from moving from an assigned position.
Oil Control Rings
The piston ring, usually located at the lower part of the piston, that prevents an excessive amount of lubricating oil from being drawn up into the combustion space during the suction stroke.
The space between the ends of the piston ring when it is in the cylinder bore.
Grooves cut in the piston barrel to hold the piston rings.
The part of the piston on the outside surface located between the piston-ring grooves.
The part of the piston below the ring belt.
Tight Piston Ring
A piston ring that will not fall in its groove under its own weight when the piston, with the ring in a horizontal plane, is turned 90 degrees (putting the ring in a vertical plane); by subsequent application of moderate finger pressure, the ring will be displaced.
Total Seal, "Technical Reference" totalseal.com